Process for stabilizing strip in a plant for coating strip material

ABSTRACT

A process for stabilizing strip in a plant for coating strip material, in which a metal strip is taken through a container holding molten coating material that has, below the melt surface, a through channel, in which induction currents are induced by an electromagnetic travelling field in the coating material and, in interaction with the electromagnetic travelling field, generate an electromagnetic force to retain the coating material. In the region of the through channel, a controllable magnetic field superimposed on the modulation of the electromagnetic travelling field is applied, whose field strength and/or frequency are adjustable as a function of sensor-detected position of the strip in the coating channel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for stabilizing strip a plant forcoating strip material, metal strip is taken through a container holdingthe molten coating material that has, below the melt surface, a throughchannel, in which induction currents are induced in the coating materialby an electromagnetic travelling wave and, in interaction with theelectromagnetic travelling field, generate an electromagnetic force toretain the coating material.

2. Discussion of the Prior Art

A plant of this type is described, for example, in German Patent 43 44939. In this case, the container that holds the molten coating materialhas an opening for the strip in the bottom. The opening is sealed by anelectromagnetic pump. The pump generates an electromagnetic force equalto or greater than the metallostatic pressure in the opening of thethrough channel. As a result, the molten material is prevented fromrunning out through the opening.

It has been found that the strip, during continuous coating, isalternately deflected or twisted. A remedy for this is not possible withconventional means, e.g., an increase in bath tension. Further rollerguides are not possible in this process area, because the coating hasnot yet solidified.

SUMMARY OF THE INVENTION

Starting from the described problems and disadvantages of the prior art,the object of the present invention is to find a process and a devicefor stabilizing strip in a generic plant, with which the strip material,without contact from outside, is brought into a more or less symmetricalposition, so that the strip does not come into contact with the walls ofthe coating channel and sustain damage as a result. The stabilization isto be adaptable to different strip widths, strip thicknesses andmaterial qualities.

To attain this object, it is proposed according to the invention that,in the region of the through channel, a controllable magnetic fieldsuperimposed on the modulation of the electromagnetic travelling fieldbe applied. The field strength and/or frequency of the controllablemagnetic field are adjustable as a function of the sensor-detectedposition of the strip in the coating channel.

The adjustable magnetic field allows the strip to be guided in thethrough channel so that the strip is introduced into the coatingmaterial without contacting the walls and without vibrations. Mechanicalguides are this not necessary.

In one embodiment of the invention, the magnetic field is controlled asa function of the sensor-detected position of the strip in the coatingchannel. Depending on the position of the strip, the magnetic field isstrengthened or weakened or unilaterally changed so that an appropriatecorrection of the strip course takes place.

Another embodiment, commonly uses the coils for the travelling fieldboth for the purpose of sealing and for that of strip stabilization. Thecoil pair or pairs are controlled by means of thyristors, which aremodulated to such an extent that a reliable seal is achieved. Dependingon the position/asymmetry of the strip detected via sensors, anadditional modulation of the coil pair or pairs is carried out for thepurpose of attaining symmetry.

A device for stabilizing strip in a generic plant is characterized bymultiple individually activatable and deactivatable magnetic coil pairsarranged on both sides of the strip in the region of coating channel,whose field strength and/or frequency are adjustable.

The magnetic coils can be arranged on both sides of the strip betweenthe coils of the electromagnetic travelling field and the opening in thecontainer bottom, for example, and can be dimensioned in keeping withthe width of the strip.

Because the magnetic coils can be individually activated anddeactivated, a more sensitive influence can be exercised on the magneticfield, and the magnetic field can be adjusted to different strip widths.

Alternatively, at least individual magnetic coils can be movablyarranged parallel to the strip surface for the purpose of deliberatelyinfluencing certain regions of the strip surface and permittingadjustment to different strip widths.

If multiple magnetic coils are arranged on each side of the strip, themagnetic coils can be activated and deactivated individually, so thatadjustment to different strip widths, thicknesses and materials ispossible within wide limits.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of the invention is shown in the drawings and describedbelow. The drawings show:

FIG. 1 is a schematic section of a container with molten coatingmaterial,

FIG. 2 shows the magnetic coil arrangement according to the invention,along with the strip along the line II-II FIG. 1 ;

FIGS. 3 shows an alternative magnetic coil.

FIG. 4 shows yet another magnetic coil arrangement; and

FIG. 5 shows still a further magnetic coil arrangement.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

FIG. 1 shows, in rough schematic fashion, a container 1 for moltencoating material 2 with a bottom opening 3 that is continued by athrough channel 4 for a strip 5 passing vertically through the container1. Arranged around the through channel 4 are coils 6, 7, in which anelectromagnetic travelling field is induced, which generates anelectromagnetic force to retain the coating material 2. Above and/orbelow these coils 6, 7, there are additional magnetic coils 8, 9 and/or10, 11, which are located on both sides of the strip 5 and the throughchannel 4 and extend over the entire width of the strip 5, as shownschematically in FIG. 2 in a cross-section through the strip 5 at thelevel of the magnetic coils 8, 9. According to the invention, themagnetic coils 8, 9 or 10, 11 can be controlled with respect to fieldstrength and/or frequency, to allow adjustments to be made to differentstrip materials or strip thicknesses.

As FIG. 3 shows, two or more individually controllable magnetic coils 8a, 8 b, 9 a, 9 b are provided on both sides of the strip 5, so as toprovide an even better influence on the strip 5 in the magnetic fieldfor stabilization according to the invention.

As FIG. 4 shows, the magnetic coils 8 a, 8 b, 9 a, 9 b are arranged at adistance from each other and are oriented toward the edge areas of thestrip 5, and are movable in both directions parallel to the stripsurface. As a result, precise adjustment to the strip width of theparticular strip 5 passing through the container can be undertaken. Themovement can be carried out hydraulically, pneumatically or by means ofelectric motor.

As FIG. 5 shows, on both sides of the strip 5, there are four magneticcoils 8 a, 8 b, 8 c, 8 d, 9 a, 9 b, 9 c, 9 d, of which the outer coils 8a, 9 a, 8 d, 9 d can be activated and deactivated depending on the stripwidth. The coils can be divided into one coil above and one below eachinductor.

To control the magnetic field, sensors can be arranged on the strip 5,for example, below the through channel 5, which, in the form of fieldstrength measurement probes or strip position probes, correspond to theentering strip 5. The strip position detected by the probes is processedin a computer into a signal, with which the magnetic coils arecontrolled.

What is claimed is:
 1. A process for stabilizing strip in a plant forcoating strip material in which a metal strip is taken through acontainer holding molten coating material and has, below a melt surface,a through channel in which induction currents are induced in the coatingmaterial by an electromagnetic travelling field generated with magneticcoils, which, in interaction with the electromagnetic travelling field,generate an electromagnetic force to retain the coating material in thecontainer, the process comprising the steps of: superimposing acontrollable magnetic field on the electromagnetic travelling field in aregion of the through channel for stabilizing the strip; andsimultaneously using the coils for the travelling field for sealing thecontainer as well as for strip stabilization so that the control of themagnetic field, which has at least one of a field strength and afrequency that is adjustable as a function of a sensor detected positionof the strip in the through channel, is superimposed on the modulationof the electromagnetic travelling field.
 2. A process as defined inclaim 1, including modulating the coil pairs via thyristors.